Thermodynamic characterization, obtained from calorimetric techniques, has been carried out in the following areas: Proteins: Stability of defatted human serum albumin and the effect of long-chain fatty acids. Nucleic Acids: Energetics of the B Yields Z transition of DNA and the contribution of the 2-amino group of adenosine to the stability of two-stranded RNA helicies has been determined. Phospholipid Membranes: The effect of anesthetics on the various phase transitions of dipalmitoylphosphatidylcholine bilayers has been delineated. Macromolecular Assembly Processes: The thermodynamic parameters of the expansion of the surface lattice in microtubules of the T4 bacteriophage capsid protein, gp23*, have been determined and interpreted at the molecular level.